Created attachment 9654[details]
tcpdump of samba session
We are upgraded from 3.6.6 on debian to 4.1.3 and notice some files become corrupted. After log investigation I notice there is error
"Oplock break failed for file main kampf.xlsx -- replying anyway"
popsup usually 10 seconds later after opening file
Googling shows up 4.1.4 also having same issue - https://bugs.freenas.org/issues/4035
So far I tried "blocking locks = no" which gives no effect.
It seems weird have some oplock break failing as only 1 user open file, samba locking itself?
I've attaching tcpdump when I open file I see this error (captured on client side)

(In reply to comment #3)
> looks as if the problem is already fixed in 4.0.15
> * BUG 10436: smbd: Fix an ancient oplock bug.
>
> Thanks!
Yep, I was just about to reply to this. Please close this bug if your problem is fixed with 4.0.15 and the pending next 4.1 release.
Thanks,
Volker

We seen corrupted files only if bytelocks are used (DB file accessed by multiply copies of application). No corruption happend to single user access documents.
Is it possible that "oplock break failed" cause this? Mark dup as for now.
*** This bug has been marked as a duplicate of bug 10436 ***